This invention generally relates to load bearing assemblies for elevator systems. More particularly, this invention relates to an arrangement for readily detecting localized strain in an elevator load bearing assembly.
Elevator systems typically include a cab and counterweight that are coupled together using an elongated load bearing member. Typical load bearing members include steel ropes and, more recently, synthetic ropes and multi-element ropes such as polymer coated reinforced belts. The increasing use of elevators in high-rise buildings has given rise to the need for an increasing use of the polymer coated reinforced belts because of their weight-to-strength ratios compared to steel roping arrangements.
Inspecting a load bearing member in an elevator system has been accomplished in several ways. With conventional steel roping, a manual, visual inspection of the rope allows the technician to determine when particular strands of the steel rope are frayed, broken or otherwise worn. This inspection method is limited, however, to the exterior portions of the rope and does not provide any indication of the condition of interior strands of the rope. Additionally, this inspection method is somewhat difficult and time consuming and does not always permit complete inspection of the entire length of the load bearing arrangement.
There are similar limitations on using visual inspection techniques on newer ropes. For example, the polymer coated reinforced belts do not permit visual inspection because of the coating that is typically applied over the cords, which are made up of strands of polymer material. Several advances have been proposed for facilitating inspection of such load bearing arrangements. One example is shown in U.S. Pat. No. 5,834,942 where a voltage detection unit is included in the load bearing member. By measuring an electrical voltage across that unit, a determination is made regarding the condition of the load bearing member. This proposal is limited, however, in that it does not provide any information regarding locations of strain along the length of the load bearing member. Moreover, there is no way of guaranteeing that a loss of conductivity through the voltage detection unit is directly correlated to strain or damage to the load bearing member. Another shortcoming of such an arrangement is that there is no qualitative information regarding degradation of the load bearing member over time.
There is a need for improved arrangements and methods for determining the condition of load bearing members in elevator assemblies. This invention provides a unique solution to that problem.